Antarctic Ice: Growing or Shrinking?

This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense.

On January 13, Nature Geoscience published an article that reports large increases in ice loss from West Antarctica over the past 10 years. It's a sobering result that's in line with earlier, independent studies.

But then why do some people say that Antarctic ice is growing?

There are three regions of Antarctic ice: the East Antarctic Ice Sheet (EAIS), the West Antarctic Ice Sheet (WAIS), and the Antarctic Peninsula. Most studies indicate that the EAIS is unchanged or growing slightly, while the WAIS and the Peninsula are losing ice.

Measurements of the entire ice sheet from 1993 to 2003 have ranged from 50 gigatons (Gt) growth per year to 200 Gt loss per year, according to the IPCC Fourth Assessment Report (IPCC AR4). But overall, the trend is towards loss of ice. Even with the higher uncertainty for Antarctica compared to Greenland, the AR4 concludes that "losses from… Antarctica have very likely contributed to sea level rise".

So why do some people imply the opposite?

The Inhofe report quotes Duncan Wingham as saying: "72% of the ice sheet covering the entire land mass of Antarctica is growing." It's hard to know for sure, but if Wingham was referring to the EAIS, he’s correct that some older studies inferred increased snow accumulation there. What's easy to miss is that Wingham said parts of the Antarctic ice sheet are growing rather than shrinking.

More than that, the most recent studies have found no evidence of increased snow accumulation on the EAIS overall.

And then there is the question of model projections versus observations. The IPCC AR4 says:

Current global model studies project that the Antarctic Ice Sheet will remain too cold for widespread surface melting and is expected to gain in mass due to increased snowfall.

This means the models made two predictions: more snow and little melt. But the IPCC also points out that recent observations don't match the model projections. Antarctic ice is, in fact, shrinking. The ice sheet models were wrong on both counts.

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Looking at the chart at the link above, it shows that the sea ice area in the Southern Hemisphere last winter was the highest it's been since satellite measurements were started in 1979 (over 16 million sq. km. Another chart from the University of Illinois site (The Cryosphere Today supported in part by NASA) shows the sea ice to be way above the 30-year average:

Now I know the Arctic sea ice was the lowest it's been in recorded history last summer, but apparently that's not happening in the southern hemisphere to SEA ICE (not surface ice). I also know that sea ice, even if it melts, won't raise sea levels, only melting surface ice that runs in the sea will raise sea levels.

Am I missing something here? Why is the sea ice in the southern hemisphere so high and so much above normal? Is this a temporary thing or is the IPCC's models actually right in saying that they don't expect much melting over much of the Antarctic? Why isn't the melting occuring as much in the south as it is in the north polar regions?

Even though the planet is in a warming mode overall, we all need to explain why some places may not be, such as the Antarctic with its large area of sea ice. As far as the western Antarctic warming and losing ice, that's a fact too, but have you seen this new study by the British Antarctic Survey reported on January 22, 2008 that says there's an active volcano under West Antarctic Ice Sheet which 'may' be aiding in its melting?

Here's part of the quote: "The first evidence of a volcanic eruption from beneath Antarctica's most rapidly changing ice sheet has been reported. The volcano on the West Antarctic Ice Sheet erupted 2000 years ago (325BC) and remains active. The subglacial volcano has a 'volcanic explosion index' of around 3-4. Heat from the volcano creates melt-water that lubricates the base of the ice sheet and increases the flow towards the sea. Pine Island Glacier on the West Antarctic Ice Sheet is showing rapid change and BAS scientists are part of an international research effort to understand this change. Using airborne ice-sounding radar, scientists from British Antarctic Survey (BAS) discovered a layer of ash produced by a 'subglacial' volcano. It extends across an area larger than Wales."

We all need to keep updated with the latest research even if it sometimes gives alternate explanations to some warming events. However, I'm still active in promoting conservation, carbon caps, reduction in energy use, increasing MPG for auto, etc. since we humans are definitely having a negative impact on the environment.

The ice cover Dr. Christy referred to was sea ice, not the Antarctic ice sheet. It’s true that last year set a record high, and there is no significant long-term trend in Antarctic sea ice extent. Why not?

The sea ice situation around Antarctica is much more complex than that in the Arctic (not that the Arctic is simple). First, there is no clear temperature trend. However, even if things were warming, the effect on sea ice might differ from the north. One explanation is that extra precipitation leads to enough freshening of the surface ocean so that the freezing point increases. Thus, sea ice may expand even with a slightly warmer ocean surface. You can learn more at this NASA site.

Thanks for the link, and for your efforts in protecting the environment.

I think another quote from a co-author of the study is important: "it cannot explain the more widespread thinning of West Antarctic glaciers that together are contributing nearly 0.2mm per year to sea-level rise."

Dr. Moore, I am all for protecting the environment, but wouldn't you also admit that since the last ice age sea levels have risen approximately 400 feet in the last 10-12,000 years so perhaps additional small levels of rising are expected, and might i say hoped for, given that we are much closer to the beginning of the next Ice Age then the end of the last one.

Plus what you are saying in terms of the sea "freshening" also means that ice cover will increase…which also implies that if Antartica gets warmer…which it is not in the interior, but if it would, lets face it, snowfall would increase….the average temp in the interior of Antarctica is if i am not mistaken minus 50 degrees, etc. far too cold for any precip. obviously if it does warm there this will result in more snowfall which will help to keep the icepack stable. bottom line is that this would keep global ocean sea levels fairly stable. plus the when the entire earth was warmer 1000 years ago and when grapes grew in Labrador and England how do you explain that when CO2 levels were lower than now.

also, for Kenzrw, i wouldn't worry about carbon caps, the data states that CO2 levels lag increases in global temp by several hundred years. in other words, CO2 increases are an EFFECT not a cause of global warming. also, livestock like cows and pigs in the U.S emit more greenhouse gases than the entire U.S fleet of autos…so if you are for some reason worried about methane and CO2 getting into the atmosphere go kill as much livestock as you can. that is a much better solution then carbon caps, which are irrelevant anyway.